Electroluminescent devices with low work function anode

ABSTRACT

Disclosed are organic electroluminescent devices employing materials of a low reduction potential in a layer functioning hole-injection. The organic electroluminescent devices may employ an anode material having a relatively low work function. Aluminum may be used in anode. During the operation, the organic electroluminescent devices may form a virtual electrode in their internal area, which enhances injection of carriers from a nearby electrode. Use of aluminum in the anode helps construction of cathode-emission organic electroluminescent devices.

RELATED APPLICATION

[0001] This application claims foreign priority based on Korean PatentApplication No. 2002-78809, filed Dec. 11, 2002, which is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to display technology. Moreparticularly, the present invention relates to organicelectroluminescent devices.

[0004] 2. Description of the Related Art

[0005] Organic luminescence or organic electroluminescence is aninstance in which electric current is converted into visible light byinternal processes of organic compounds. Organic compounds having eitherfluorescent or phosphorescent characteristics generate light emissionupon the application of electric current. Both organic fluorescent andphosphorescent molecules are referred to as organic light-emittingcompounds.

[0006] An organic luminescent or electroluminescent device is generallycomposed of two opposing electrodes and at least one layer interposedbetween the two electrodes. The at least one layer between theelectrodes contains at least one organic light-emitting compound.Electrons and holes, collectively referred to as carriers, are injectedinto the layer from the two electrodes, which are a cathode and ananode. Upon application of appropriate electric power, the cathode is toinject electrons toward the interposed layer, while anode is to injectholes toward the same layer.

[0007] Performance of organic electroluminescent devices depends on,among many factors, the quantity of the carriers injected from theelectrodes. The more the carriers are injected, the more likely to havehigh luminescence or brightness. To inject a large number of carriersfrom the electrodes at a low driving voltage, materials for theelectrodes are chosen such that the carriers are easily injectedtherefrom. The anode is generally made from materials having a high workfunction. The cathode is generally made from materials having a low workfunction. In a single electroluminescent device, the work function ofthe anode material is higher than that of the cathode material.

[0008] Further, to inject a larger number of carriers from theelectrodes at a low driving voltage, carrier-injecting layers may beintroduced. The carrier-injecting layers are to facilitate injection ofcarriers from the electrodes. A hole-injecting layer may be formed onthe side of the anode, facing the cathode. An electron-injecting layermay be formed on the side of the cathode, facing the anode. Materialsfor the carrier-injecting layers are also chosen such that thecarrier-injecting layers easily receive carriers from the electrodes.The hole-injecting layer is generally made from materials having a lowoxidation potential, which are easily oxidized at a low electricpotential applied. The electron-injecting layer is generally made frommaterials having a low reduction potential, which are easily reduced ata low electric potential applied.

SUMMARY OF THE INVENTION

[0009] One aspect of the present invention provides variouselectroluminescent devices. According to one embodiment of the presentinvention, an electroluminescent device comprises: a cathode; an anodeopposing the cathode, the anode comprises a material having a workfunction not greater than about 4.5 eV; and a functional layer locatedbetween the anode and cathode, the functional layer comprises a chemicalcompound of Formula I:

[0010] In the formula, R1-R6 are independently chosen from the groupconsisting of hydrogen, halo, nitrile (—CN), nitro (—NO₂), sulfonyl(—SO₂R), sulfoxide (—SOR), sulfonamide (—SO₂NR), sulfonate (—SO₃R),trifluoromethyl (—CF₃), ester (—CO—OR), amide (—CO—NHR or —CO—NRR′),straight-chain or branched (substituted or unsubstituted) C₁-C₁₂ alkoxy,straight-chain or branched (substituted or unsubstituted) C₁-C₁₂ alkyl,aromatic or non-aromatic (substituted or unsubstituted) heterocyclic,substituted or unsubstituted aryl, mono- or di-(substituted orunsubstituted)aryl-amine, and (substituted orunsubstituted)alkyl-(substituted or unsubstituted)aryl-amine.

[0011] In the above described device, the work function of the materialin the anode ranges from about 3.5 eV to about 4.5 eV. The chemicalcompound has a reduction potential ranged from about −0.6V to about 0 V.The chemical compound is more stable in a reduced state thereof than ina neutral state thereof. The chemical compound has an electron mobilityfrom about 10⁻¹⁰ cm/V.s to about 10⁻⁵ cm/V.s. The chemical compound hasa hole mobility from about 10⁻⁴ cm/V.s to about 1 cm/V.s. The chemicalcompound is Formula Ia:

[0012] Still in the above described device, the functional layer isconfigured to facilitate movement of charge carriers from the anode in adirection toward the cathode. The functional layer substantiallycontacts the anode. The anode is made substantially of one or moreconductive materials, and wherein the device further comprises anintervening layer between the functional layer and the anode. Theintervening layer comprises one or more metallic oxides. The functionallayer comprises the chemical compound of Formula I in an amount rangingfrom 1 wt % to 100 wt %. The functional layer has a thickness from 0.1nm to 10,000 nm. The device further comprises a light-emitting layerbetween the cathode and the functional layer. The device furthercomprises a substrate, wherein the anode is located between thesubstrate and the functional layer. The anode comprises a transparentmaterial. The anode comprises a metal oxide material. The device furthercomprises a substrate, wherein the cathode is located between thesubstrate and the functional layer. The cathode comprises a transparentmaterial. The anode comprises an opaque material. The anode comprises areflective material having a reflectivity from about 0.3 to about 1. Thereflective material is reflective to substantially all wavelengths ofvisible light. The anode comprises at least one material selected fromthe group consisting of aluminum, silver, platinum, chromium and nickel.The anode comprises aluminum.

[0013] According to another embodiment, the electroluminescent devicecomprises: a cathode; an anode opposing the cathode, the anode comprisesa substantially reflective material; and a functional layer locatedbetween the anode and cathode, the functional layer comprises a chemicalcompound of Formula I defined above. The substantially reflectivematerial has a reflectivity from about 0.4 to about 1. The substantiallyreflective material is selected from the group consisting of aluminum,silver, gold, nickel, chromium, molybdenum, tantalum, titanium, andzinc. The substantially reflective material is reflective tosubstantially all of the wavelength components of visible light.

[0014] According to another embodiment, the electroluminescent devicecomprises: an anode formed substantially of a conductive material havinga work function not greater than about 4.5 eV; a cathode electrodeopposing the anode and formed substantially of a conductive material; atleast one light-emitting layer located between the anode and cathode;wherein the anode is configured to inject holes in a direction towardthe at least one light-emitting layer, whereas the cathode is configuredto inject electrons in a direction toward the at least light-emittinglayer; a buffer layer contacting either the anode or cathode on a sidethereof toward the at least one light-emitting layer; and wherein thebuffer layer is formed substantially of at least one substantiallynon-conductive material. The buffer layer contacts the anode. The anodecomprises aluminum, and wherein the buffer layer comprises aluminumoxide. The device further comprises a hole-injecting layer locatedbetween the buffer layer and the at least one light-emitting layer,wherein the hole-injecting layer comprises a chemical compound ofFormula I as defined above. The device further comprises another bufferlayer contacting the cathode and located between the cathode and the atleast one light-emitting layer. The buffer layer has a substantiallysmall thickness sufficient to allow holes to pass therethrough. Thebuffer layer has a thickness from about 5 Å to about 40 Å. The bufferlayer has a thickness from about 10 Å to about 20 Å.

[0015] In the above-described device, the at least one substantiallynon-conductive material is selected from the group consisting ofaluminum oxide, titanium oxide, zinc oxide, ruthenium oxide, nickeloxide, zirconium oxide, tantalum oxide, magnesium oxide, calcium oxide,strontium oxide, vanadium oxide, yttrium oxide, lithium oxide, cesiumoxide, chromium oxide, silicon oxide, barium oxide, manganese oxide,cobalt oxide, copper oxide, praseodymium oxide, tungsten oxide,germanium oxide, potassium oxide, lithium fluoride, magnesium fluoride,cesium fluoride, calcium fluoride, sodium chloride, potassium chloride,lithium metaborate (BiBO₂), potassium silicate (K₂SiO₃),silicon-germanium oxides, barium titanate, lithium tantalate (LiTaO₃),silicon nitride (Si₃N₄), boron nitride (BN), nitrides of elements inFamily III or IV of the Periodic Table of the Elements, zinc sulfide(ZnS), cadmium sulfide (CdS), cadmium selenide (CdSe), gallium phosphide(GaP) and gallium nitride (GaN).

[0016] According to still another embodiment, the electroluminescentdevice comprises: an anode comprises an anode material; a cathodescomprises a cathode material; at least one layer between the anode andthe cathode; and wherein the anode material has the work function lessthan or substantially equal to the work function of the cathodematerial. The anode material and the cathode material are the same. Theat least one layer comprises a chemical compound of Formula I asdescribed above. The at least one layer comprises a chemical compound ofFormula Ia as defined above.

[0017] According to still another embodiment, the electroluminescentdevice comprises: an anode; a cathode; an anode contacting layercontacting the anode between the anode and cathode; a cathode contactinglayer contacting the cathode between the anode and cathode; and meansfor forming a virtual electrode within at least one of the anodecontacting layer and the cathode contacting layer.

[0018] Another aspect of the present invention provides variouselectronic displays. The displays comprises the above-describedelectroluminescent devices according to various embodiments. Thedisplays further comprises an electronic circuit connected to theelectroluminescent devices.

[0019] Another aspect of the present invention provides a method ofoperating an electronic device, comprises: providing an electronicdevice comprises an anode, a cathode and a functional layer between theanode and cathode, the functional layer having an interface with theanode or an intervening layer located between the anode and thefunctional layer; applying a forward bias electric power between theanode and cathode; and wherein electrons are injected from the anodeinto the functional layer and substantially stay in an area near theinterface, thereby forming a virtual cathode.

[0020] In the above-described method, a continued application of theforward bias electronic power facilitates injection of holes from theanode into the functional layer. A continued application of the forwardbias electronic power facilitates transportation of holes within thefunctional layer in a direction toward the cathode. The functional layercomprises a material having a reduction potential (low), electronmobility (low), hole mobility (high). The functional layer comprises achemical compound of Formula I as described above. The functional layercomprises a chemical compound of Formula Ia as defined above. Thefunctional layer comprises at least one chemical compound having areduction potential ranged from about −0.4V to about 0 V. The functionallayer comprises at least one chemical compound having a reductionpotential ranged from about −0.3V to about 0 V. The anode comprises atleast one material having a work function ranges from about 3.5 eV toabout 4.5 eV. The functional layer comprises at least one chemicalcompound having an electron mobility therein lower than about 10⁻⁵cm/V.s. The functional layer comprises at least one chemical compoundhaving an electron mobility therein from about 10⁻¹⁰ cm/V.s to about10⁻⁶ cm/V.s. The functional layer comprises at least one chemicalcompound having a hole mobility therein higher than about 10⁻⁴ cm/V.s.The functional layer comprises at least one chemical compound having ahole mobility therein from about 10⁻⁴ cm/V.s to about 1 cm/V.s.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIGS. 1-6 illustrate simplified cross-sectional views of organicEL devices in accordance with embodiments of the present invention.

[0022]FIG. 7 illustrates formation of a virtual cathode in an electronicdevice in accordance with an embodiment of the present invention.

[0023]FIG. 8 illustrates a simplified cross-sectional view of an activematrix driven organic EL device in accordance with an embodiment of thepresent invention

[0024]FIG. 9 illustrates a simplified crosss-sectional view of anorganic EL device employing a non-conductive sublayer in its anode inaccordance with an embodiment of the present invention.

[0025]FIG. 10 illustrates voltage-current relationship in the operationof the devices of Examples 7 and 8.

[0026]FIG. 11 illustrates voltage-current relationship in the operationof the devices of Examples 9 and 10.

[0027]FIG. 12 illustrates voltage-current relationship in the operationof the devices of Examples 11 and 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Now the various aspects of the present invention will bediscussed in more detail in terms of embodiments. It is to be understoodat the outset of the description that persons of skill in theappropriate arts may modify the invention described here while stillachieving the favorable results of this invention. Accordingly, thefollowing description is to be understood as being a broad, teachingdisclosure directed to persons of skill in the appropriate arts, and notas limiting upon the present invention. The headings used in thefollowing description are merely to generally refer to the contents oftheir following discussions, but do not define or limit the contents ofthe discussions.

[0029] Constructions of Organic EL Devices

[0030] Organic EL devices in accordance with various embodiments of thepresent invention can be constructed in various ways. Generalconstruction of the organic EL devices includes two opposing electrodesand one or more functional layers interposed between the electrodes. Theterm “layer” refers to a deposit, coat or film of one material or amixture of two or more materials. FIGS. 1-6 illustrate exemplarycross-sectional constructions of the organic EL devices that can embodyvarious aspects of the present invention. In these drawings, the samereference numbers are used to indicate like layers or components amongthe constructions. It should be noted that these constructions are notexhaustive variants of the organic EL devices in accordance of thepresent invention.

[0031] The illustrated organic EL devices 10 has a substrate 1, an anode3, a cathode 15 and one or more functional layers located between theanode 3 and the cathode 15. The one or more intervening functionallayers include a hole-injecting layer 5, a hole-transporting layer 7, alight-emitting layer 9, an electron-transporting layer 11, anelectron-injecting layer 13 and multi-functional layers having functionsof two or more of the foregoing layers. A non-exhaustive list of themulti-functional layers includes a layer with hole-injecting andhole-transporting functions, a layer with hole-injecting andlight-emitting functions, a layer with hole-injecting, hole-transportingand light emitting functions, a layer with electron-injecting andelectron-transporting functions, a layer with electron-transporting andlight-emitting functions, a layer with electron-injecting,electron-transporting and light-emitting functions, and so forth.

[0032] The substrate 1 (FIGS. 1-6) supports the laminated structure ofthe organic EL device 10. Although the drawings show that the substrate1 is located on the side of the anode 3, the substrate 1 may be locatedon the side of the cathode 15. In either case, the substrate 1 providesa support on which the laminated construction of the organic EL devicecan be built during the manufacturing. The anode 3 (FIGS. 1-6) andcathode 15 (FIGS. 1-6) are electrically connected to an electric powersource 17 (FIGS. 1-6) via a switch 19 (FIGS. 1-6), which is controlledby a controller (not shown). Although not illustrated, either or both ofthe electrodes 3 and 15 may be formed in multiple layers, which may ormay not include a non-conductive layer, which is often called “a bufferlayer”. The hole-injecting layer 5 (FIGS. 1-3) is to facilitate theinjection of holes from the anode 3 into the hole-transporting layer 7(FIGS. 1-5). Similarly, the electron-injecting layer 13 (FIGS. 1 and 4)is to facilitate the injection of electrons from the cathode 15 into theelectron-transporting layer 13. The hole-transporting layer 7 is toaccelerate movement of holes away from the anode 3 and/or thehole-injecting layer 5 toward the light-emitting layer 9 (FIGS. 1-6).The electron-transporting layer 11 (FIGS. 1, 2, 4 and 5) is toaccelerate movement of electrons away from the cathode 15 and/or theelectron-injecting layer 13 toward the light-emitting layer 9 (FIGS.1-6). With regard to the functional layers and other features of organicEL devices, refer to U.S. patent application Publication No. ______ ofU.S. patent application Ser. No. 10/099,781, filed Mar. 14, 2002 andU.S. patent application Publication No. ______ of U.S. patentapplication Ser. No. 10/431,349, filed May 6, 2003, the publications ofwhich are hereby incorporated herein by reference in its entirety.

[0033] When applying an appropriate electric voltage between theelectrodes 3 and 15, electrons and holes are injected from the cathode15 and anode 3, respectively, into intervening layer(s). The holes andelectrons travel to and recombine at light-emitting molecules located inthe intervening layer. Recombined pairs of electrons and holes, namelyexcitons, transfer the energy of the recombination to the light-emittingmolecules where they recombined. Alternatively, excitons move around fora short period of time and transfer the recombination energy to otherlight-emitting molecules, particularly to those having a smaller bandgap than the light-emitting molecules where they recombined. Thetransferred energy is used to excite valence electrons of thelight-emitting molecules, which generates photons when the electronsreturn to their ground state.

[0034] Organic EL Devices Using Compound of Formula I

[0035] One aspect of the present invention provides organic EL devicescontaining at least one compound represented by Formula I in one or moreof the functional layers between the two opposing electrodes 3 and 15.

[0036] In Formula I, R1-R6 are independently chosen from the groupconsisting of hydrogen, halo, nitrile (—CN), nitro (—NO₂), sulfonyl(—SO₂R), sulfoxide (—SOR), sulfonamide (—SO₂NR), sulfonate (—SO₃R),trifluoromethyl (—CF₃), ester (—CO—OR), amide (—CO—NHR or —CO—NRR′),straight-chain or branched (substituted or unsubstituted) C₁-C₁₂ alkoxy,straight-chain or branched (substituted or unsubstituted) C₁-C₁₂ alkyl,aromatic or non-aromatic (substituted or unsubstituted) heterocyclic,substituted or unsubstituted aryl, mono- or di-(substituted orunsubstituted)aryl-amine, and (substituted orunsubstituted)alkyl-(substituted or unsubstituted)aryl-amine. In theforegoing substituent groups, R and R′ are, for example, substituted orunsubstituted C₁-C₆₀ alkyl, substituted or unsubstituted aryl,substituted or unsubstituted 5-7 membered heterocyclic. The substitutedC₁-C₆₀ alkyl, aryl and heterocyclic are optionally substituted with oneor more of amine, amide, ether and ester groups. Alternatively, R1-R6are independently selected from substituted or unsubstituted electronwithdrawing substituent groups, which are well understood by those ofordinary skill in the art. The aryl group includes phenyl, biphenyl,terphenyl, benzyl, naphthyl, anthracenyl, tetracenyl, pentacenyl,perylenyl and coronenyl, which are singly or multiply substituted orunsubstituted.

[0037] Non-limiting examples of the Formula I compounds are shown belowas Formula Ia through Formula If.

[0038] Other examples of Formula I, synthesis of such compounds andvarious features of the compounds are further disclosed in U.S. PatentApplication Publication No. US 2002/0158242 A1, and U.S. Pat. Nos.6,436,559 and 4,780,536, all of which are hereby incorporated herein byreference in their entirety.

[0039] In an embodiment of the present invention, the organic EL device10 includes at least one of the compounds of Formulas Ia-If. Optionally,at least one of the compound of Formulas Ia-If is contained in any ofthe layers singly or in combination with one or more compounds ofFormula I or others. Still optionally, the compound of Formula Ia iscontained in at least one of the layers of the organic EL device 10singly or in combination with one or more other compounds, which may ormay not be compounds represented by Formula I.

[0040] Generally, compounds of Formula I may be used in any of thefunctional or multi-functional layers of the organic EL device 10.Optionally, the compounds are those of Formula Ia-If. Optionally, one ormore compounds represented by Formula I are contained in any of thelayers contacting the anode 3. In one embodiment, the organic EL deviceincludes a hole-injecting layer 5 as illustrated in FIGS. 1-3, and atleast one of the compounds represented by Formula I is contained in thathole-injecting layer 5. Optionally, the hole-injecting layer is formedwith at least one compound represented by Formula I substantially freeof other materials. Alternatively, the hole-injecting layer is formedwith at least one of the compounds represented by Formula I incombination with one or more other materials.

[0041] In another embodiment, the organic EL device includes ahole-transporting layer 7 as illustrated in FIGS. 1-5, and at least oneof the compounds represented by Formula I is contained in thehole-transporting layer 7. Optionally, the compounds are those ofFormula Ia-If. Optionally, the hole-transporting layer is formed with atleast one compound of Formula I either substantially free of othermaterials or in combination with one or more other materials. In anotherembodiment, the organic EL device includes a layer for the functionsincluding hole-injection and hole-transportation, and thismulti-functional layer contains at least one compound represented byFormula I. This multi-functional layer is formed with at least onecompound of Formula I either substantially free of other materials or incombination with one or more other materials.

[0042] Virtual Electrode

[0043] Another aspect of the present invention relates to formation of avirtual electrode in the operation of electronic devices includingorganic EL devices. The term “virtual electrode” is to refer to chargecarrier accumulation in an internal area of an electronic device when itis viewed like an electrode from the perspective of a real electrode.The virtual electrode enhances or facilitates injection of the carriersfrom the real electrode.

[0044] Now the formation of a virtual electrode is discussed withreference to an exemplary organic EL device 16 construction of FIG. 7.Although the discussion is in the context of EL devices, the virtualelectrode is not a phenomenon unique only in organic EL devices, but canoccur in any other electronic devices. The organic EL device 16 includesan anode 3 and a cathode 15 that are opposingly located. Each electrode3 and 15 is connected to the power source 17 with a control switch 19. Afirst layer 21 and a second layer 23 are interposed between the opposingelectrodes 3 and 15. At least one of the first and second layers 21 and23 contain a light emitting material.

[0045] Without wishing to be bound for any theory of why the inventionworks, in one embodiment, the first layer 21 is made of a material thatis more stable in its reduced state than its neutral state. Here, amaterial is more stable in its reduced state than its neutral state ifthe material spontaneously turns to its reduced state from its neutralstate. Further suppose, for example, that electrons have very lowmobility in the material of the first layer 21 while holes are highmobility therein. When the contact between the anode 3 and the firstlayer 21 is formed, free electrons of the anode 3 are transferred to thefirst layer 21 and for reduction of the material of the first layer 21.Because of poor electron mobility in the material, the transferredelectrons hardly travel within the first layer 21 after crossing overthe border 27 between the anode 3 and the first layer 21. Rather, thetransferred electrons stay near the border 27 on the side of the firstlayer 21. Accordingly, the electrons transferred from the anode 3 to thefirst layer 21 accumulate along the border 27 as illustrated withreferenced with number 25.

[0046] From the perspective of the anode 3, the accumulated electrons ornegative charges 25 along the border 27 are viewed as if the source ofelectrons, that is, the cathode of the device, is located very close tothe border 27 because of the abundance of negative charges. In thatsense, the area of the accumulated electrons 25 is called a virtualcathode. When applying a forward bias between the electrodes 3 and 15 bythe operation of the switch 19, the anode 3 injects holes toward thevirtual cathode 25 and therefore toward the first layer 21. Thecloseness of the negative charges of the virtual cathode from the anode3 facilitates the injection of holes from the anode 3. The holesinjected into the first layer 21 moves forward in the direction towardthe real cathode 15 or the second layer 23 with the momentum of theinjection from the anode 3 and with the forward bias between the twoelectrodes 3 and 15. The high hole mobility of the material for thefirst layer 21 helps the transportation of the holes in the directiontoward the real cathode 15 or the second layer 23.

[0047] A similar phenomenon may occur in the second layer 23 to form avirtual anode by accumulation of holes along the border 29 between thecathode 15 and the second layer 23. The material for the second layer 23are selected from those which are more stable in its oxidized state thanits neutral state, and have low hole mobility and high electron mobilitytherein. Holes are transferred from the cathode 15 to the second layer23 and accumulate near the border between the cathode 15 and the secondlayer 23. The accumulated holes are viewed as a virtual anode from theperspective of cathode 15. Upon application of an appropriate electricpower in a forward bias, the cathode 15 will inject electrons into thesecond layer 23.

[0048] In accordance with various embodiments of the present invention,charge carriers accumulate in an internal area of the device to form avirtual electrode. In the organic EL device 16 (FIG. 7), for example,the first layer 21 may constitute a hole-injecting layer, ahole-transporting layer, a light-emitting layer or a multi-functionallayer with the functions of the foregoing layers. Alternatively, thefirst layer 21 may not exist, and the anode 3 contacts the second layer23. The second layer 23 may constitute, for example, a hole-transportinglayer, a light-emitting layer, an electron-transporting layer, anelectron-injecting layer or a multi-functional layer with one or morefunctions of the foregoing layers. Alternatively, the second layer 23may not exist, and the cathode 15 contacts the first layer 21. Althoughthe phenomenon is discussed in terms of the organic EL device having oneor two of the layers 21 and 23, the same applies in any otherconstructions of organic EL devices, for example, having more than twolayers interposed between the anode 3 and cathode 15.

[0049] In the embodiment of the organic EL device forming a virtualelectrode, the first layer 21 contains a chemical compound which is morestable in its reduced state than its neutral state. Optionally, such achemical compound is selected from the compounds represented by FormulaI. Preferably, the first layer contains the compound of Formula Ia. Inanother embodiment, a chemical compound for the first layer 21 has areduction potential from about −0.6 Volts (V) to about 0 V, preferably,from about −0.2 V to about 0 V. Alternatively, the reduction potentialof the compound for the first layer 21 is from about −0.3 V to about 0V, optionally from about −0.1 to about 0 V. The first layer 21 containsa chemical compound, in which electrons have low mobility while holeshave high mobility. The compound for the first layer 21 has electronmobility equal to or lower than about 10⁻⁵ cm/V.s, preferably from about10⁻¹⁰ cm/V.s to about 10⁻⁶ cm/V.s. The compound for the first layer 21has hole mobility equal to or higher than about 10⁻⁴ cm/V.s, preferablyfrom about 10⁻⁴ cm/V.s to about 1 cm/V.s.

[0050] In an embodiment of the organic EL device forming a virtualelectrode, the second layer 23 contains a chemical compound, which ismore stable in its oxidized state than its neutral state. In anotherembodiment, the second layer 23 contains a chemical compound for thesecond layer 23 has an oxidation potential equal to or lower than about0.5 V. Alternatively, the oxidation potential of the compound is fromabout 0 to about 0.4 V, preferably, from about 0 to about 0.3 V. Thesecond layer 23 contains a chemical compound, in which holes have lowmobility while electrons have high mobility. The compound for the secondlayer 23 has hole mobility equal to or lower than about 10⁻⁴ cm/V.s,preferably from about 10⁻¹⁰ cm/V.s to about 10⁻⁵ cm/V.s. The compoundfor the second layer 23 has electron mobility equal to or higher thanabout 10⁻⁵ cm/V.s, preferably from about 10⁻⁵ cm/V.s to about 1 cm/V.s.

[0051] Work-Function of Electrode Materials

[0052] Another aspect of the present invention relates to use of amaterial having a low work function in the anode 3. It has been generalknowledge in the relevant art that materials for an anode are selectedfrom those having a relatively high work function; on the other hand,materials for a cathode are selected from those having a relatively lowwork function. In accordance with an embodiment of the presentinvention, however, an organic EL device has an anode, the material ofwhich has a relatively low work function. For example, the work functionof the anode material is below about 4.5 eV, preferably below about 4.3eV. Alternatively, the work function of the anode material is from about3.5 eV to about 4.5 eV, preferably from about 3.8 eV to about 4.3 eV.The materials for use in an anode includes, for example, aluminum (Al,4.28 eV), silver (Ag, 4.26 eV), zinc (Zn, 4.33 eV), niobium (Nb, 4.3eV), zirconium (Zr, 4.05 eV), tin (Sn, 4.42 eV), tantalum (Ta, 4.25 eV),vanadium (V, 4.3 eV), mercury (Hg, 4.49 eV), gallium (Ga, 4.2 eV),indium (In, 4.12 eV), cadmium (Cd, 4.22 eV), boron (B, 4.4 eV), hafnium,(Hf, 3.9 eV), lanthanum (La, 3.5 eV), niobium (Nb, 4.3 eV), titanium(Ti, 4.3 eV) or alloys of one of above metals with neodymium (Nd) orpalladium (Pd).

[0053] One possible, but non-limiting explanation for the use of arelatively low work-function material in an anode is that the lowwork-function anode material helps formation of the above-describedvirtual cathode. Referring back to FIG. 7, the low work-functionmaterial of the anode 3 easily transfers electrons to the first layer 21upon formation of the contact between the anode 3 and the first layer21. The electron transfer from the anode 3 to the first layer 21 isenhanced upon application of an appropriate voltage. The electronstransferred into the first layer 21 form the virtual cathode 25, whichenhances the hole injection from the anode 3 into the first layer 21 andin the direction toward the real cathode 15 as described above.

[0054] According to an embodiment of the present invention, the workfunction of the cathode material is below about 4.5 eV. The materialsfor use in the cathode 15 include, for example, magnesium, calcium,sodium, potassium, titanium, indium, yttrium, lithium, gadolinium,aluminum, silver, tin, lead, similar metals, CsF, alloys containing oneor more of the foregoing metals, or multiple layers containing one ormore of the foregoing metals including LiF/Al and Li₂O/Al. Eithertransparent or non-transparent materials may be used for the cathode 15,depending upon the construction of the light passage in the organic ELdevice as discussed above. Those of ordinary skill in the art wouldappreciate any other materials that can be used in the cathode 15 andalso the selection of appropriate cathode materials.

[0055] According to an embodiment of the present invention, the anode 3has a single layered construction formed of a single material, which canbe a substantially pure elemental material or a homogeneous ornon-homogeneous alloy. In another embodiment, the anode 3 may includemultiple sublayers, which may or may not include a non-conductivesublayer. Optionally, the discussion above of the work function of anodematerials apply only to conductive part of the anode 3, not to anon-conductive sublayer or part thereof. Optionally, the anode 3 mayhave one or more conductive material sublayers. In the case of the anodeconstruction including multiple conductive material sublayers, thediscussion above of the work function of anode materials applies to atleast one of the conductive materials.

[0056] Another aspect of the present invention relates to use of amaterial having a high work function in the cathode 15. Just like thelow work-function anode, the high work-function cathode material helpsformation of the above-described virtual anode. In accordance with anembodiment of the present invention, an organic EL device 10 has acathode 15, the material of which has a high work function. For example,the work function of the cathode material is above about 3.5 eV,preferably above about 4 eV. Alternatively, the work function of thecathode material is from about 4.1 eV to about 5.0 eV, preferably fromabout 4.1 eV to about 4.8 eV.

[0057] Reflective Materials for Anode

[0058] Another aspect of the present invention relates to the use ofreflective material in the anode 3 of an organic EL device. In anembodiment of the organic EL device according to the present invention,the anode is formed with one or more materials having high reflectivity.For example, the reflectivity as a ratio of a reflected light intensityto an inputted light intensity is above about 0.2, for example fromabout 0.4 to about 1. Reflective materials for use in the anode 3include, for example, aluminum, silver, gold, nickel, chromium,molybdenum, tantalum, titanium, and zinc. Optionally, the materials havethe reflectivity to substantially all of the wavelength components ofvisible light. Optionally, the materials have substantially evenreflectivity to substantially all of the wavelength components ofvisible light. Preferably, the reflective anode materials are, forexample, aluminum, silver, platinum, chromium and nickel.

[0059] In an embodiment of the present invention, the anode 3 mayinclude a plurality of sublayers. Optionally, the anode 3 may be formedof at least one transparent sublayer and a reflective sublayer. The atleast one transparent sublayer may be formed with transparent materials,for example, including ITO (indium tin oxide), IZO (indium zinc oxide),and fluorinated tin oxide. The reflective sublayer is formed with one ormore reflective materials as described above. As an alternativeembodiment, the anode 3 is a single layer made of a reflective material.The single layer construction of the anode is advantageous over themulti-sublayer construction in terms of the simplicity in themanufacturing process.

[0060] Top Emission

[0061] In the constructions of FIGS. 1-6 where the anode 3, not thecathode 15, contacts the substrate 1, the use of reflective material inthe anode 3 allows the generated light to emit through the cathode 15 orin a direction other than through the anode 3. In the same constructionsof FIGS. 1-6, the emission through the cathode 15 is referred to as topemission; on the other hand, the emission through the anode 3 andsubstrate 1 is referred to as bottom emission. Optionally, the organicEL device 10 may be constructed in the top emission design. For topemission, the cathode 15 is substantially transparent.

[0062] In one embodiment, the substantially transparent cathode 15 isformed in a single layer of one or more transparent conductivematerials. Examples of the transparent conductive materials include ITO(indium tin oxide), IZO (indium zinc oxide) and fluorinated tin oxide.Alternatively, the substantially transparent cathode 15 is formed inmultiple layers (not shown). For example, the cathode 15 in the multiplelayer construction may include a thin layer made of a normallynon-transparent material and a transparent material layer. The thinlayer of the normally non-transparent material is formed in a thicknessthrough which the visible light emitted from an organic EL material canpass. Optionally, the thickness of the thin layer is from about 10 Å toabout 500 Å, preferably from about 10 Å to about 200 Å. The normallynon-transparent materials for use in the thin layer include, forexample, magnesium (Mg), calcium (Ca), lithium (Li), aluminum (Al),indium (In), potassium (K), yttrium (Y), strontium (St), europium (Eu),sodium (Na), gallium (Ga), samarium (Sm) or an alloy or mixture of twoor more of the foregoing elements. The transparent material layer ismade of one or more materials, which are, for example, indium tin oxide(ITO), indium zinc oxide (IZO) and fluorinated tin oxide. The thicknessof the transparent material layer is from about 100 Å to about 5000 Å.The cathode 15 in the multiple layer construction may further includeone or more additional layers.

[0063] Location and Kind of Control Circuits

[0064] The top emission design of organic EL devices is generally morecompatible with active matrix driving of the devices than the bottomemission design. The active matrix driving requires a layer 31 for atransistor or an integrated circuit between the substrate 1 and theanode 3 as illustrated in FIG. 8. In organic EL devices with the bottomemission design, the integrated circuit layer 31 will block at leastsome of the light emitted from the light-emitting compound. However, thetop emission design would not be affected by the existence of theintegrated circuit layer 31 below the anode 3. Nor would the topemission design be affected by the technology of forming the integratedcircuit layer 31, for example use of amorphous silicon or polysilicon,which affects the aperture ratio of the layer 31.

[0065] In the embodiment of top emission design, the organic EL devicesutilize either passive matrix or active matrix circuit design.Optionally, the top emission design utilizes active matrix circuitdesign. Still optionally, the integrated circuit for the active matrixdriving is formed between the substrate 1 and the anode 3. Stilloptionally, the integrated circuit is formed with the amorphous silicontechnology.

[0066] Sealing Layer

[0067] In certain embodiments of organic EL devices, it is advantageousto have a sealing layer between the substrate 1 and the anode 3 toprevent moisture or other contaminating substances from permeating intothe intricate area of laminated structure. Such a sealing layer is moreimportant particularly when the material for the substrate 1 is morepermeable. The sealing layer is often made with one or moresubstantially non-permeable or semi-permeable materials. Such materialsare, for example, aluminum, aluminum oxide, strontium oxide, bariumoxide, silicon oxide, silicon nitride. The sealing layer may beconstructed in multiple layers including at least one organic sub-layerand at least one inorganic sub-layer. An organic sub-layer may be formedwith, for example, polyphenylethylene, polymerized epoxy compoundsand/or polycyclicalkane. An inorganic sub-layer may be formed with, forexample, silicon nitride, silicon oxide and/or barium oxide. To theextent that the substantially non-permeable or semi-permeable materialcan also be used as an anode material, the anode 3 itself forms thesealing layer. Thus, no separate sealing layer need to be formed. In anembodiment of the present invention, the anode 3 is made of aluminum,aluminum-neodymium alloy or aluminum-palladium alloy, which functions assealing layer as well. The anode 3 that also functions as a sealinglayer is used together with any appropriate substrate materials with orwithout intervening integrated circuit layer 31 between the substrate 1and the anode 3.

[0068] Non-Conductive Sublayer of Anode

[0069] In any organic EL device embodiments of present invention, eitheror both of the anode 3 and cathode 15 may be formed in multiplesublayers. Referring to FIG. 9, for example, the anode 3 of theillustrated organic EL device includes a conductive sublayer 33 and anon-conductive sublayer 35. Although shown in two sublayers, the anode 3may have more than two sublayers. As illustrated, the non-conductivesublayer 35 is located between the conductive sublayer 33 and thehole-injecting layer 5, which contacts the anode 3 on its side towardthe cathode 15. The hole-injecting layer 5 in this laminated anodeconstruction can be substituted for a hole-transporting layer 7 (FIGS. 4and 5), a light-emitting layer 9 (FIG. 6) or a multi-functional layer(not shown). In the alternative, the non-conductive sublayer 35 may beconsidered as a separate layer inserted between the anode 3 and thelayer 5, 7 or 9 contacting the anode 3.

[0070] Considered as a separate layer, the non-conductive sublayer 35may be referred to as a buffer layer. Regardless of its name, thenon-conductive sublayer or buffer layer 35 is formed to improveinterfacial strength between the conductive sublayer 33 (or anode 3) andthe layer 5, 7 or 9 contacting the anode 3. The non-conductive sublayeror buffer layer 35 also help lowering the energy barrier for theinjection of holes from the conductive sublayer 33 into the layer 5,7,or 9 contacting the non-conductive sublayer 35. In an embodiment, thenon-conductive sublayer or buffer layer 35 is formed with one or moreinorganic materials. Optionally, the materials for the buffer layerinclude, for example, aluminum oxides, titanium oxides, zinc oxides,ruthenium oxides, nickel oxides, zirconium oxides, tantalum oxides,magnesium oxides, calcium oxides, strontium oxides, vanadium oxides,yttrium oxides, lithium oxides, cesium oxides, chromium oxides, siliconoxides, barium oxides, manganese oxides, cobalt oxides, copper oxides,praseodymium oxides, tungsten oxides, germanium oxides, potassiumoxides, lithium fluoride, magnesium fluoride, cesium fluoride, calciumfluoride, sodium chloride, potassium chloride, lithium metaborate(BiBO₂), potassium silicate (K₂SiO₃), silicon-germanium oxides, bariumtitanate, lithium tantalate (LiTaO₃), silicon nitride (Si₃N₄), boronnitride (BN), nitrides of elements in Family III or IV of the PeriodicTable of the Elements, zinc sulfide (ZnS), cadmium sulfide (CdS),cadmium selenide (CdSe), gallium phosphide (GaP), gallium nitride (GaN)and combinations of two or more of the foregoing materials.

[0071] Manufacturing the Device

[0072] Various layers of the organic EL devices of the present inventioncan be produced by utilizing any film forming techniques, includingsputtering, electron beam vapor deposition, other types of physicalvapor depositions (PVD), chemical vapor deposition (CVD), spin coating,dip coating, doctor blading, inkjet printing, screen-printing,roll-coating and thermal transfer. These techniques are generallydescribed in the following publications, which are hereby incorporatedherein by reference: Applied Physics Letters, 73, 18, 1998, 2561-2563;Applied Physics Letters, 78, 24, 2001, 3905-3907. Persons of ordinaryskill in the art would appreciate the appropriate film formingtechniques under the conditions and circumstances for the formation ofsuch layers.

EXAMPLES

[0073] Various aspects and features of the present invention will befurther discussed in terms of the examples. The following examples areintended to illustrate various aspects and features of the presentinvention but not to limit the scope of the present invention.

Example 1

[0074] A glass substrate (Corning 7059) was coated with about 1300 Åindium tin oxide (ITO) and was ultrasonically cleaned in an aqueoussolution of a cleaning agent from Fischer Co. The cleaned ITO layeredsubstrate was dried and transferred to a plasma cleaning device. Thesubstrate was further cleaned with argon-oxygen (2:1) plasma at 50 Wunder 14 m torr for 5 minutes. The substrate was then transferred to avacuum vapor deposition chamber.

[0075] About 100 Å of aluminum layer is deposited on the ITO layer bythermal vacuum vapor deposition to form a semitransparent aluminumanode. The aluminum layer is exposed to oxygen gas under atmosphericpressure for 5 minutes to form an aluminum oxide layer of about 20 Å. Ahole-injecting layer of the compound of Formula Ia (hexanitrilehexaazatriphenylene or HAT) was formed over the aluminum oxide layer atabout 500 Å by thermal vacuum deposition. Over the hole-injecting layer,a hole-transporting layer was formed with NPB at about 400 Å by thermalvacuum deposition. Over the hole-transporting layer, a light-emittinglayer was formed with Alq3 at about 300 Å by thermal vacuum deposition.Over the light-emitting layer, an electron-transporting layer was formedwith the compound of Formula II(2-[4-[(N-phenylbenzimidazol-2-yl)phenyl-9,10-bis(2-naphtyl)anthracene]at about 200 Å by thermal vacuum deposition. For the cathode, a layer ofabout 10 Å of lithium fluoride (LiF) was formed over theelectron-transporting layer, and then a layer of about 2500 Å aluminumwas further deposited. During the deposition, the pressure within thedeposition chamber was maintained at 5-8×10⁻⁷ torr. The organicmaterials were deposited at the speed of 1 Å/sec. The lithium fluoridewas deposited at the speed of 0.3 Å/sec, and the aluminum was depositedat a speed of 3-7 Å/sec.

[0076] The resulting laminated structure of the organic EL device wasrepresented as “Glass substrate/ITO(1300 Å)/Al(100 Å)/Al₂O₃(20Å)/HAT(500 Å)/NPB(400 Å)/Alq3(300 Å)/Formula II(200 Å)/LiF(10 Å)/Al(2500Å).” When 5.17 V of forward bias was applied across the resultingdevice, 500 nit of emission was observed through the semitransparentaluminum layer. The color of the emission was identified as x=0.460,y=0.550 in the 1931 CIE color coordination. The current density duringthe operation was 50 mA/cm².

Example 2

[0077] A device was fabricated in the same manner as in Example 1 exceptthat the ITO layer was not formed and that the Al₂O₃ layer was notformed. The resulting structure was represented as “Glasssubstrate/Al(10 Å)/HAT(500 Å)/NPB(400 Å)/Alq3(300 Å)/Formula II(200Å)/LiF(10 Å)/Al(2500 Å).”

[0078] When 5.0 V of forward bias was applied across the resultingdevice, 1,010 nit of emission was observed through the semitransparentaluminum layer. The color of the emission was identified as x=0.417,y=0.534 in the 1931 CIE color coordination. The current density duringthe operation was 50 mA/cm².

Example 3

[0079] A device was fabricated in the same manner as in Example 1 exceptthat the hole-injection layer of HAT was not formed. The resultingstructure of the device was represented as “Glass substrate/ITO(1300Å)/Al(100 Å)/Al₂O₃(20 Å)NPB(400 Å)/Alq3(300 Å)/Formula II(200 Å)/LiF(10Å)/Al(2500 Å).” No emission was observed even when applying over 20 Vforward bias to the device. The current density during the applicationof the forward bias was less than 0.1 mA/cm².

Example 4

[0080] A device was fabricated in the same manner as in Example 1 exceptthat the aluminum and aluminum oxide layers between the ITO and NPB werenot formed. The resulting structure was represented as “Glasssubstrate/ITO(1300 Å)/HAT(500 Å)/NPB(400 Å)/Alq3(300 Å)/Formula II(200Å)/LiF(10 Å)/Al(2500 Å).” When 5.37 V of forward bias was applied acrossthe resulting device, green emission of the color x=0.345, y=0.553 ofthe 1931 CIE color coordination was observed. The current density duringthe operation was 50 mA/cm². At 100 mA/cm² of constant DC currentdensity, it took 23 hours until the brightness drops to 80% level of theinitial brightness of 3399 nit.

Example 5

[0081] A device was fabricated in the same manner as in Example 1 exceptthat 100 Å thickness of silver was formed as a semitransparent anodeinstead of aluminum and aluminum oxide. The resulting structure of thedevice was represented as “Glass substrate/ITO(1300 Å)/Ag(100 Å)/HAT(500Å)/NPB(400 Å)/Alq3(300 Å)/Formula II(200 Å)/LiF(10 Å)/Al(2500 Å).” When5.1 V of forward bias was applied across the resulting device, observedwas 800 nit of emission of the color x=0.420, y=0.516 of the 1931 CIEcolor coordination. The current density during the operation was 50mA/cm².

Example 6

[0082] A device is fabricated in the same manner as in Example 5 exceptthat the ITO layer is not formed. The resulting structure is representedas “Glass substrate/Ag(100 Å)/HAT(500 Å)/NPB(400 Å)/Alq3(300 Å)/FormulaII(200 Å)/LiF(10 Å)/Al(2500 Å).” When a forward bias is applied acrossthe resulting device, visible light is observed

Example 7

[0083] A glass substrate (Corning 7059) coated with about 1300 Å indiumtin oxide (ITO) was ultrasonically cleaned in an aqueous solution of acleaning agent from Fischer Co. The cleaned ITO layered substrate wasdried and transferred to a plasma cleaning device. The substrate wasfurther cleaned with argon-oxygen (2:1) plasma at 50 W under 14 m torrfor 5 minutes. The substrate was then transferred to a vacuum vapordeposition chamber.

[0084] The compound of Formula Ia (hexanitrile hexaazatriphenylene orHAT) was formed over the ITO layer at about 2000 Å by thermal vacuumdeposition. Over the compound layer, about 500 Å aluminum was depositedto form cathode. During the deposition, the pressure within thedeposition chamber was maintained at 5-8×10⁻⁷ torr.v. The organicmaterials were deposited at the speed of 1 Å/sec and the aluminum wasdeposited at a speed of 3-7 Å/sec.

[0085] The resulting laminated structure of the organic EL device wasrepresented as “Glass substrate/ITO(1300 Å)/HAT(2000 Å)/Al(500 Å).” Whena forward bias was applied across the device, electric current wasobserved at a potential difference just above 0 V. The voltage-currentrelationship was shown in FIG. 10.

Example 8

[0086] A device was fabricated in the same manner as in Example 7 exceptthat 1600 Å thickness of NPB was formed instead of HAT. The resultingstructure of the device was represented as “Glass substrate/ITO(1300Å)/NPB(1600 Å)/Al(500 Å).” When a forward bias was applied across thedevice, electric current was observed at a potential difference about 1V. The voltage-current relationship was also shown in FIG. 10.

Example 9

[0087] A device was fabricated in the same manner as in Example 7 exceptthat 500 Å aluminum layer was formed as an anode in lieu of the ITOlayer. The resulting structure was represented as “Glasssubstrate/Al(500 Å)/HAT(2000 Å)/Al(500 Å).” When a forward bias wasapplied across the device, electric current was observed at a potentialdifference just above 0 V. The voltage-current relationship was shown inFIG. 11.

Example 10

[0088] A device was fabricated in the same manner as in Example 9 exceptthat 2000 Å thickness of NPB was formed instead of HAT. The resultingstructure of the device was represented as “Glass substrate/Al(500Å)/NPB(2000 Å)/Al(500 Å).” When a forward bias was applied across thedevice, no electric current was observed even at a potential differenceover 20 V. The voltage-current relationship was also shown in FIG. 11.

Example 11

[0089] To the device fabricated in the Example 9 having the constructionof “Glass substrate/Al(500 Å)/HAT(2000 Å)/Al(500 Å),” an electricpotential was applied with the opposite polarity to that of Example 9,in which the aluminum located between the glass substrate and HAT layeracted as a cathode, and the aluminum located above the HAT acted as ananode. Upon the application of the forward bias, the current started toflow just above 0 V. The voltage-current relationship was also shown inFIG. 12. The result in combination with that of Example 9 indicate thatthe HAT layer enabled the aluminum layer to inject holes into it whetherthe aluminum layer is deposited below or above the HAT layer.

Example 12

[0090] To the device fabricated in the Example 10 having theconstruction of “Glass substrate/Al(500 Å)/NPB(2000 Å)/Al(500 Å),” anelectric potential was applied with the opposite polarity to that ofExample 10, in which the aluminum located between the glass substrateand NPB layer acted as a cathode, and the aluminum located above the HATacted as an anode. When the forward bias was applied, almost no currentwas observed at a potential difference of above 20V. The voltage-currentrelationship was also shown in FIG. 12.

What is claimed is:
 1. An electroluminescent device, comprising: acathode; an anode opposing the cathode, the anode comprising a materialhaving a work function not greater than about 4.5 eV; and a functionallayer located between the anode and cathode, the functional layercomprising a chemical compound of Formula I:

wherein R1-R6 are independently chosen from the group consisting ofhydrogen, halo, nitrile (—CN), nitro (—NO₂), sulfonyl (—SO₂R), sulfoxide(—SOR), sulfonamide (—SO₂NR), sulfonate (—SO₃R), trifluoromethyl (—CF₃),ester (—CO—OR), amide (—CO—NHR or —CO—NRR′), straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkoxy, straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkyl, aromatic or non-aromatic(substituted or unsubstituted) heterocyclic, substituted orunsubstituted aryl, mono- or di-(substituted orunsubstituted)aryl-amine, and (substituted orunsubstituted)alkyl-(substituted or unsubstituted)aryl-amine.
 2. Thedevice of claim 1, wherein the work function of the material in theanode ranges from about 3.5 eV to about 4.5 eV.
 3. The device of claim1, wherein the chemical compound has a reduction potential ranged fromabout −0.6V to about 0 V.
 4. The device of claim 1, wherein the chemicalcompound is more stable in a reduced state thereof than in a neutralstate thereof.
 5. The device of claim 1, wherein the chemical compoundhas an electron mobility from about 10⁻¹⁰ cm/V.s to about 10⁻⁵ cm/V.s.6. The device of claim 1, wherein the chemical compound has a holemobility from about 10⁻⁴ cm/V.s to about 1 cm/V.s.
 7. The device ofclaim 1, wherein the chemical compound is Formula Ia:


8. The device of claim 1, wherein the functional layer is configured tofacilitate movement of charge carriers from the anode in a directiontoward the cathode.
 9. The device of claim 1, wherein the functionallayer substantially contacts the anode.
 10. The device of claim 1,wherein the anode is made substantially of one or more conductivematerials, and wherein the device further comprises an intervening layerbetween the functional layer and the anode.
 11. The device of claim 10,wherein the intervening layer comprises one or more metallic oxides. 12.The device of claim 1, wherein the functional layer comprises thechemical compound of Formula I in an amount ranging from 1 wt % to 100wt %.
 13. The device of claim 1, wherein the functional layer has athickness from 0.1 nm to 10,000 nm.
 14. The device of claim 1, furthercomprising a light-emitting layer between the cathode and the functionallayer.
 15. The device of claim 1, further comprising a substrate,wherein the anode is located between the substrate and the functionallayer.
 16. The device of claim 1, wherein the anode comprises atransparent material.
 17. The device of claim 1, wherein the anodecomprises a metal oxide material.
 18. The device of claim 1, furthercomprising a substrate, wherein the cathode is located between thesubstrate and the functional layer.
 19. The device of claim 1, whereinthe cathode comprises a transparent material.
 20. The device of claim 1,wherein the anode comprises an opaque material.
 21. The device of claim1, wherein the anode comprises a reflective material having areflectivity from about 0.3 to about
 1. 22. The device of claim 21,wherein the reflective material is reflective to substantially allwavelengths of visible light.
 23. The device of claim 1, wherein theanode comprises at least one material selected from the group consistingof aluminum, silver, platinum, chromium and nickel.
 24. The device ofclaim 1, wherein the anode comprises aluminum.
 25. A display comprising:the electroluminescent device of claim 1; and an electronic circuitconnected to the electroluminescent device.
 26. An electroluminescentdevice, comprising: a cathode; an anode opposing the cathode, the anodecomprising a substantially reflective material; and a functional layerlocated between the anode and cathode, the functional layer comprising achemical compound of Formula I:

wherein R1-R6 are independently chosen from the group consisting ofhydrogen, halo, nitrile (—CN), nitro (—NO₂), sulfonyl (—SO₂R), sulfoxide(—SOR), sulfonamide (—SO₂NR), sulfonate (—SO₃R), trifluoromethyl (—CF₃),ester (—CO—OR), amide (—CO—NHR or —CO—NRR′), straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkoxy, straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkyl, aromatic or non-aromatic(substituted or unsubstituted) heterocyclic, substituted orunsubstituted aryl, mono- or di-(substituted orunsubstituted)aryl-amine, and (substituted orunsubstituted)alkyl-(substituted or unsubstituted)aryl-amine.
 27. Thedevice of claim 26, wherein the substantially reflective material has areflectivity from about 0.4 to about
 1. 28. The device of claim 26,wherein the substantially reflective material is selected from the groupconsisting of aluminum, silver, gold, nickel, chromium, molybdenum,tantalum, titanium, and zinc.
 29. The device of claim 26, wherein thesubstantially reflective material is reflective to substantially all ofthe wavelength components of visible light.
 30. An electronic displaycomprising: the electroluminescent device of claim 26; and an electroniccircuit connected to the electroluminescent device.
 31. Anelectroluminescent device, comprising: an anode formed substantially ofa conductive material having a work function not greater than about 4.5eV; a cathode electrode opposing the anode and formed substantially of aconductive material; at least one light-emitting layer located betweenthe anode and cathode; wherein the anode is configured to inject holesin a direction toward the at least one light-emitting layer, whereas thecathode is configured to inject electrons in a direction toward the atleast light-emitting layer; a buffer layer contacting either the anodeor cathode on a side thereof toward the at least one light-emittinglayer; and wherein the buffer layer is formed substantially of at leastone substantially non-conductive material.
 32. The device of claim 31,wherein the buffer layer contacts the anode.
 33. The device of claim 32,wherein the anode comprises aluminum, and wherein the buffer layercomprises aluminum oxide.
 34. The device of claim 32, further comprisinga hole-injecting layer located between the buffer layer and the at leastone light-emitting layer, wherein the hole-injecting layer comprises achemical compound of Formula I:

wherein R1-R6 are independently chosen from the group consisting ofhydrogen, halo, nitrile (—CN), nitro (—NO₂), sulfonyl (—SO₂R), sulfoxide(—SOR), sulfonamide (—SO₂NR), sulfonate (—SO₃R), trifluoromethyl (—CF₃),ester (—CO—OR), amide (—CO—NHR or —CO—NRR′), straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkoxy, straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkyl, aromatic or non-aromatic(substituted or unsubstituted) heterocyclic, substituted orunsubstituted aryl, mono- or di-(substituted orunsubstituted)aryl-amine, and (substituted orunsubstituted)alkyl-(substituted or unsubstituted)aryl-amine.
 35. Thedevice of claim 32, further comprising another buffer layer contactingthe cathode and located between the cathode and the at least onelight-emitting layer.
 36. The device of claim 31, wherein the bufferlayer has a substantially small thickness sufficient to allow holes topass therethrough.
 37. The device of claim 31, wherein the buffer layerhas a thickness from about 5 Å to about 40 Å.
 38. The device of claim31, wherein the buffer layer has a thickness from about 10 Å to about 20Å.
 39. The device of claim 31, wherein the at least one substantiallynon-conductive material is selected from the group consisting ofaluminum oxide, titanium oxide, zinc oxide, ruthenium oxide, nickeloxide, zirconium oxide, tantalum oxide, magnesium oxide, calcium oxide,strontium oxide, vanadium oxide, yttrium oxide, lithium oxide, cesiumoxide, chromium oxide, silicon oxide, barium oxide, manganese oxide,cobalt oxide, copper oxide, praseodymium oxide, tungsten oxide,germanium oxide, potassium oxide, lithium fluoride, magnesium fluoride,cesium fluoride, calcium fluoride, sodium chloride, potassium chloride,lithium metaborate (BiBO₂), potassium silicate (K₂SiO₃),silicon-germanium oxides, barium titanate, lithium tantalate (LiTaO₃),silicon nitride (Si₃N₄), boron nitride (BN), nitrides of elements inFamily III or IV of the Periodic Table of the Elements, zinc sulfide(ZnS), cadmium sulfide (CdS), cadmium selenide (CdSe), gallium phosphide(GaP) and gallium nitride (GaN).
 40. A display comprising: theelectroluminescent device of claim 31; and an electronic circuitconnected to the electroluminescent device.
 41. An electroluminescentdevice comprising: an anode comprising an anode material; a cathodescomprising a cathode material; at least one layer between the anode andthe cathode; and wherein the anode material has the work function lessthan or substantially equal to the work function of the cathodematerial.
 42. The device of claim 41, wherein the anode material and thecathode material are the same.
 43. The device of claim 41, wherein theat least one layer comprises a chemical compound of Formula I:

wherein R1-R6 are independently chosen from the group consisting ofhydrogen, halo, nitrile (—CN), nitro (—NO₂), sulfonyl (—SO₂R), sulfoxide(—SOR), sulfonamide (—SO₂NR), sulfonate (—SO₃R), trifluoromethyl (—CF₃),ester (—CO—OR), amide (—CO—NHR or —CO—NRR′), straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkoxy, straight-chain or branched(substituted or unsubstituted) C₁-C₁₂ alkyl, aromatic or non-aromatic(substituted or unsubstituted) heterocyclic, substituted orunsubstituted aryl, mono- or di-(substituted orunsubstituted)aryl-amine, and (substituted orunsubstituted)alkyl-(substituted or unsubstituted)aryl-amine.
 44. Thedevice of claim 41, wherein the at least one layer comprises a chemicalcompound of Formula Ia:


45. A display comprising the electroluminescent device of claim
 41. 46.An organic electroluminescent device, comprising: an anode; a cathode;an anode contacting layer contacting the anode between the anode andcathode; a cathode contacting layer contacting the cathode between theanode and cathode; and means for forming a virtual electrode within atleast one of the anode contacting layer and the cathode contactinglayer.